A series of Chandra images has allowed scientists to
trace the evolution of large-scale X-ray jets produced
by a black hole in a binary star
system. As the schematic shows, gaseous matter
pulled from a normal star forms a disk around the black
hole. The gas is heated to temperatures of millions of
degrees, and intense electromagnetic forces in the disk
can expel jets of high-energy particles.

An outburst of X-rays from the source, XTE J1550-564,
was detected by NASA's Rossi X-ray Timing Explorer (RXTE) in 1998.
Further observations with Chandra and radio telescopes detected
first one jet (left), then another opposing jet (right)
of high-energy particles moving away from the black
hole at about half the speed of light. Four years after
the outburst, the jets had moved more than 3 light
years apart with the left jet slowing down and
disappearing.

The observations indicate that the jet on the left is
moving along a line tilted toward Earth, whereas the
jet on the right is tilted away from Earth. This
alignment explains why the left jet appears to have
traveled farther from the black hole than the jet on
the right, and why the left jet faded first.

However, with this alignment, the relative brightness
of the right jet is difficult to understand because it
is receding, and should be dimmer than it appears. One
explanation is that it is plowing into a dense cloud of
gas. The resistance of the gas would slow down the jet,
and produce a shock wave that could energize the
electrons in the jet, causing it to brighten. The
observed cometary shape of the right jet indicates that
it is in fact interacting with interstellar gas.

The ejection of jets from stellar black holes and
supermassive black holes is a common occurrence in the
universe, and appears to be one of the primary ways
that black holes inject energy into their environment.
Although all jets are assumed to decelerate because of
the resistance of the gas through which they move, the
process can take millions of years for jets from
supermassive black holes.

The XTE J1550 jets are the first ones caught in the
act of slowing down. During the past four years
astronomers have observed a process that would take as
much as a million years to unfold for a supermassive
black hole jet. This underscores the enormous value of
studying black holes in our galaxy such as XTE
J1550.